With the trend toward a healthy lifestyle worldwide, a variety of studies have been made to elucidate the physiological effects of fat or oil. Conjugated linoleic acid, for example, is found to have a therapeutic effect on diabetes or syndrome X as well as an anti-obesity effect and anti-tumor effect (Patent Documents 1 to 5 and Non-patent Document 1). Conjugated linoleic acids having such effects are reported to be applicable to foods (Patent Document 6).
On the other hand, diacylglycerol is found to have an anti-obesity effect and the like (Patent Documents 7 and 8). Moreover, there is a fat or oil known as containing diacylglycerol having a high content of specific fatty acid such as ω3 fatty acid or linoleic acid (Patent Documents 9 to 11).
Besides, a fat or oil composition obtained by a combination of diacylglycerol and phytosterol is found to have an effective ability to improve the cholesterol level in blood (Patent Document 12).
Conjugated linoleic acid is thought to be not suitable either for easy digestion or as a food, because this acid belongs to a family of free fatty acids and therefore itself has a foreign taste peculiar to free fatty acids. Such a circumstance spurred attempts to open up the spectrum of applications of conjugated linoleic acids by using its ester form (Patent Documents 13 to 18) (Non-patent Documents 2 and 3).    [Patent Document 1] WO 96/06605    [Patent Document 2] WO 97/46230    [Patent Document 3] JP-A-2003-171272    [Patent Document 4] WO 02/009691    [Patent Document 5] WO 02/009693    [Patent Document 6] WO 00/21379    [Patent Document 7] JP-A-04-300826    [Patent Document 8] JP-A-10-176181    [Patent Document 9] WO 01/109899 WO 01/10989    [Patent Document 10] WO 02/11552    [Patent Document 11] EP 0679712A    [Patent Document 12] WO 99/48378    [Patent Document 13] WO 00/64854    [Patent Document 14] WO 04/96748    [Patent Document 15] JP-A-2003-113396    [Patent Document 16] U.S. Pat. No. 6,432,453    [Patent Document 17] U.S. Pat. No. 6,608,222    [Patent Document 18] EP 1097708A    [Non-patent Document 1] Lipids, 32, 853-858 (1997)    [Non-patent Document 2] Biotechnology Letters, 20(6), 617-621 (1998)    [Non-patent Document 3] Biotechnol. Prog., 20, 619-622 (2004)